The family business is known to get in the way, often, of Reagan family relations.

So it was again as Season 4 of the CBS police drama
"Blue Bloods" began Friday (Sept. 27) with "Unwritten Rules." The hour opened as Jamie (
Will Estes) got a new patrol partner in Edit "Eddie" Janko (
"Pretty Little Liars" alum
Vanessa Ray), a new graduate of the police academy.

"You're my first, Reagan," she told him. "Be gentle." It didn't take her long to leap into her new job, though, since a "shots fired" alert sent her scurrying into their car's driver's seat to speed to the scene.

Once they arrived, more shots rang out as they were being briefed on a jewelry-store robbery, and Jamie found a female officer down. While he scanned the area for the shooter, Eddie got a taste of the emotionality she was in for by seeing a photo of the felled officer's husband and daughter.Â

As Frank (
Tom Selleck) arrived at the hospital later, the doctor told him, "We did everything we could. She died a few minutes ago." And on his way to the hospital chapel to talk to the officer's survivors, Frank stated to the victim's waiting peers -- including Jamie -- "We're going to get this son of a b****."

At the shooting site, Danny (
Donnie Wahlberg) learned recently paroled convict Angelo (
Malcolm Goodwin) was seen running from the scene. New police chief Dino Arbogast (
John Ventimiglia) told Frank he knew the victim, to which Frank reaffirrned about the probe, "Whatever it takes."

A senior citizen tried to identify the suspect from mug shots, and her uncertainty led Danny to "help" her. When his partner Maria (
Marisa Ramirez) questioned that afterward, he told her, "When someone takes out a cop, all bets are off."

The duo then headed for Grand Central Station upon getting a tip that someone matching Angelo's description was there, leading to a chase and a takedown by Danny. But looking at a lineup back at the precinct, the elderly witness only could muster, "I'm pretty sure that's him."

Erin (
Bridget Moynahan) also observed the lineup and told Danny that Angelo's attorney would have the witness "for lunch" in court. She knew she'd need more to make a case, but Danny tried to convince her of the circumstantial evidence, prompting raised voices between the Reagan siblings.

"This guy's a cop-killer, and you're worried about your batting average?" he accused. "Give me something I can use, and I will charge" the suspect, she replied. "Until then, he is free to go."

Danny and Maria turned their attention to finding a second suspect, and Frank wasn't happy to learn Erin was behind letting Angelo go. He also wasn't thrilled to have to order police protection for Angelo, who was claiming harassment (including a brick through his window), but Frank knew any hint of impropriety by his officers had to be avoided.

He then called Jamie to ask if he'd be willing to be assigned to that detail, knowing his son also was a lawyer. And in another moment of Reagan vs. Reagan, a tight-lipped Jamie said, "Do what you have to do, Commissioner."

Erin felt heat from her boss, who seemed willing to bend rules to get Angelo charged, stressing the importance of the relationship between the D.A.'s office and the NYPD. "You fix this," a conflicted Erin was ordered.

Danny and Maria tried to find a second suspect in the robbery by tracking down his heroin supplier ... and upon locating the dealer, they found him with some of the stolen jewelry. Thus, they got information on Suspect No. 2, who made a run for it as police invaded his hiding place.

Cornered, the suspect told Danny and others, "I'm not dying in jail." And as he reached for a gun he had tucked in his pants, an officer shot him multiple times ... and he died without identifying Angelo as his accomplice.

The first Reagan family dinner of the new season followed the slain officer's funeral, and it was a tense affair. Erin stated, "Obviously, some of you are mad at me," and though Linda (
Amy Carlson) was ready to send her and Danny's sons (
Tony and
Andrew Terraciano) to another room -- a familiar move, as "Blue Bloods" fans know -- Erin felt they should stay and learn what a lawyer "can and cannot do."

Danny wasn't satisfied with her explanation, and Jamie was disgruntled that in guarding Angelo, "He's laughing in our faces." Even normally calming Reagan patriarch Henry (
Len Cariou) lashed out at Erin, and she then asked Frank point-blank if he also felt she was betraying her family. "I think you were in a tough spot," he said diplomatically, "and you felt what you did was right."

That wasn't good enough for Erin, who got up from the table -- though her daughter Nicky (
Sami Gayle) had defended her -- and left by telling her relatives, "Clearly, I'm not welcome here. And for the record, loyalty is a two-way street."

At the courthouse, Erin's boss was alarmed that several officers from the murdered cop's precinct failed to show up to testify in cases. "'Blue flu' is bad for business," she told Erin. And when Erin responded that they could be forced to appear, the boss advised her, "When your house is on fire, don't reach for the gasoline."

Frank demanded to know from Dino who was behind the "blue flu" and ordered that officer's suspension, then asked Dino why he hadn't informed Frank about the matter himself. A debate between Frank's right-hand man Garrett (
Gregory Jbara) and Dino ensued, with Frank ending it by declaring, "'Blue flu' stops now."

At a restaurant, Frank was approached by Erin. Inviting her to sit, he acknowledged, "Cops and prosecutors have different sets of rules." He then recalled a high-school relay in which Erin had dropped a baton, adding that when that happens, "Both runners are responsible." And reminding her Danny was doing all he could to ensure justiice, Frank asked her, "Are you?"

As their watch over Angelo continued, Jamie and Eddie saw the slain officer's partner and two colleagues apparently seeking their charge in very evident rage. Jamie talked the partner down, saying, "You've gotta go through me." And Eddie joined him despite her earlier reluctance, adding, "Me, too."

Danny arrived at work the next day to find Erin waiting. After a few more heated words, she said, "Neither of us did our best work here." He sheepishly agreed, and she asked for his help in getting the cop-killer off the street.

Danny was interrogating Angelo again when Erin walked in to offer a seven-year sentence, with parole in five. Danny seemed outraged, and Erin cautioned Angelo that if rejected the deal, the alternative would be a first-degree-murder trial. Angelo agreed to write a statement ... and after they left the room, Erin and Danny showed they'd been pulling a good-cop, bad-cop act.

The catch? If Angelo's confession didn't specifically reject the deal she'd offered, Erin would have to honor it. And if that happened, she admitted to Danny, "I'll have a lot more free time on my hands."

Dino met Frank at a cemetery that was the resting place of many police officers, and Frank told him he had "crossed a line" in condoning the "blue flu" campaign. Frank told him that in performing what his job was, he'd have to make many tough decisions. "I get that," Dino replied. "No, you don't ... but you will," Frank said, adding that if Dino ever withheld "vital information from me again, you'll be gone in a heartbeat."

Angelo was ready to agree to Erin's deal, until Danny mentioned his accomplice had never given him up. The cocky Angelo said, "Then you've got no case," and rejected the deal. Erin confirmed that Danny heard it, then added -- with the written confession she held -- "Please book him on a charge of Murder One."

After their shift, Eddie told Jamie she respected him for how he'd handled the revenge-seeking officer earlier in the day. And as he watched her get into her clearly expensive sports car, she explained it was a high-school graduation present from her father: "Don't hold it against me."

Back at the Reagan homestead, Erin dropped in on Frank, Danny, Jamie and Henry, telling them she "could use a drink." As he poured it, Frank told them, 'It''s sometimes easy to forget we're all on the same side." And they collectively drank a toast to "all the fallen," including Reagan son Joe.